since the fish is considered killed when between the fins the area of a sela coin dries (shulchan aruch harav 316.13)
probably the only option that you gave that will work is "Holding the fish in a bowl"
ps maybe a wet towel will work
the maharal mi prag brings that the source of kaparot from gemoro is the Rabbi Akiva (ish gam zu)'s story with the donkey chicken and candle (last paragraph on the page, if you are lazy you can start from the end next page 7 lines from the end of the fist paragraph)
opinion that main thing in the kaporos is shechita (see last paragraph on the page)